What happened
On 20 September 2018, a Boeing 737-800, registration VT-JGS, operating a scheduled flight from Mumbai to Jaipur, experienced a serious cabin pressure incident. During the climb through 10,000 feet, the flight crew noticed a rapid increase in cabin altitude, which was soon followed by a cabin altitude warning. The crew immediately donned oxygen masks and initiated a descent to 10,000 feet.
While managing the situation, the pilot flying switched the engine bleed switches to the ON position. This action, combined with the manual pressurization settings, led to a sudden change in cabin pressure. Upon landing back in Mumbai, it was discovered that 21 passengers had suffered nosebleeds or ear pain, with some passengers later diagnosed with hemotympanum due to barotrauma.
The investigation
AAIB India's investigation focused on the sequence of events that allowed the aircraft to depart with the engine bleed switches in the OFF position. The inquiry examined maintenance records, flight recorder data, and cockpit procedures. The investigation included a flight simulation at a training complex to understand the pressure fluctuations experienced during the descent and the subsequent activation of the outflow valve.
Findings
- The incident originated during a maintenance task performed the previous day, where an aircraft maintenance engineer left the engine bleed switches in the OFF position after monitoring pack temperatures.
- The flight crew failed to identify the incorrect switch positions during the pre-flight scan.
- During both the "Before Take-off" and "After Take-off" checklists, the crew performed the challenge and response without visually verifying the actual position of the bleed switches.
- The primary cause was the failure to restore the bleed switches to the ON position following maintenance, compounded by multiple checklist verification failures by the flight crew.
- The crew's decision to turn the bleeds ON while in manual mode, without properly managing the outflow valve, contributed to the rapid pressure changes that caused passenger injuries.
- There was a lack of communication between the flight deck and the cabin crew regarding the nature of the technical situation.
Safety action
- The airline is encouraged to emphasize the importance of strict checklist adherence and the dangers of complacency during training and refresher courses.
- The importance of Crew Resource Management (CRM) must be reinforced to prevent oversight during high-workload phases.
- Airport operators should improve communication protocols to ensure the specific scale of medical assistance required is relayed to ground agencies in real time.